I was looking at these pistons http://www.summitracing.com/parts/sl...make/chevrolet. it says theyre flat, but with valve reliefs. For calculating compression ratio, would i just assume 0 for dome/dish?

 

No you'll need to know how dished they are with valve reliefs. It's usually something on the order of 4ccs.

Edit: I looked mine up, which are exactly the same style (forged Keith Blacks though not summit) and they're dished 4ccs with the valve reliefs.

 

I have googled the crap out of these pistons and can't seem to find what the CC is on them. I even looked on Federal Mogul's website and it didn't post those specs. Anyone know for sure what they are?

 

I would assume 5cc if they're the same as most other sealed power 4 valve relief pistons.

Why are you not at least going with a hypereutectic piston?

 

My main reason is cost, and I'm not planning on putting out a huge amount of power. I would love to step up on pistons, but this is definitely a budget build. If I could get a set of hypereutectic pistons for close to the same price, I would.

 

Have you checked to see if pistons for a 3.48 stroke are cheaper?

 

Hypereutectic pistons for a 3.48 stroke are cheaper than the cast ones for 3.25 stroke.

 

If you're going with the cheeeeeeepest of the cheeeeeeeeep just because it's cheeeeeeeeeeeep, what DIFFERENCE does the volume make? It's CHEEEEEEEEEEEEP.

Those will have 5 - 6 cc of "dish" volume; and don't forget to include the extra .020" of deck clearance they have, in addition the .025" or so that comes stock. I.e., at TDC, the top of them will still be .045" shy of the deck.

There's ALOT of tolerance in a stock block though; could end up anywhere between about .040" and about .055", and might even vary that much from one cyl to another.

And that's BEFORE the uncertainty in the stroke for each cyl, and the possibility for different rod lengths (which you can GUARANTEE will be shorter than stock, because they don't make a rod stretcher) are taken into account. Those can easily add another .010" of deck clearance.

Which is all just one small part of the reason why anybody that quotes their CR out to 2 decimal places, OBVIOUSLY (a) didn't measure it, and (b) doesn't know what they're doing.

Building a 327 is idiotic. You can buy a 350 crank at the parts store for the same price as having your 327 one turned, plus the $25 core charge. Pistons will probably be enough CHEEEEEEEEEEEPER that you might even be able to MAKE MONEY by adding the other 25 CID. As long as it's a large-journal block, it'll all drop right in.

Don't shoot yourself in the foot building that even smaller motor because it's "different" or because it's "free" or even because you're "cheeeeeeeeeeeeep".

 

I believe the question was what cc would be for the pistons, not; is building a 327 stupid. People like you make these forums miserable for people that just want there question answered.

The best way to get your most accurate answer call summit, there are some 4 valve relief pistons that are 8cc.

 

I belive the question was alot more along the lines of, "what pistons should I buy"; and the right answer is, "ones for a 1.56" compression height instead of 1.65" CH".

The driving force here seems to be, CHEEEEEEEEEEP.

Pistons with the 1.56" CH are CHEEEEEEEEEEEEEEEEEPER than ones with a 1.65" CH because there's about 500 times more of them running around. Enough CHEEEEEEEEEEEEEEPER in fact, that the difference WILL PAY FOR the different crank, and maybe, THEN SOME. IOW, d00d can very possibly PUT MONEY IN HS POCKET while simultaneously GETTING MORE by a better choice of other parts.

People like you make these forums miserable for those of us who have BEEN THERE and DONE THAT and would like to pass along the benefit of our ACCUMULATED EXPERIENCE (which you plainly LACK) so that people with less experience can avoid having to learn THE SAME LESSONS us old geezers had to learn BY SCREWING UP back before Algore invented the Interwebz. You also make these forums miserable for those who are trying to learn. It's easier to help people out when we don't have ... this sort of thing to contend with.

Given the tolerances surrounding the whole issue of the CCs of valve reliefs, the difference between 4 or 5 or 6 or 8 is "measure with micrometer, mark with spray paint, cut with explosives". Just putting some old garbage heads on this thing that started out with anywhere from 75 to 80 CCs, like the uncertainties in crap like 882, 993 or 624, and have done nothing but GET MORE UNCERTAIN with time and machine sodomization, will SWAMP any such tiny variation in "cheeeeeeeeeeeep" pistons.

Best way to find out what the CCs is, is to ask here, and let those of us who have BEEN THERE and DONE THAT speak to our EXPERIENCE from when we have measured stuff.

 

Well I guess I'm an idiot for building a 327...... now that that's out there, another reason I am doing it (also budget) is because I'm sticking a T-5 trans behind it for now, and a 327 is going to have less torque than a 350.

Back to the original question (can we keep "I hate 327 and you're CHEEEEEEEEEEEP" opinions out from now on?)

 

You can always cc the valve reliefs, but that wont tell you how far in the hole the pistons are.



But for the sake of a baseline, I would assume 5.

If you're doing it so cheap you have to buy plain cast pistons you really ought to consider building a cheaper 350. But do whatever makes you happy, man, because in the end thats what it's all about.